BlueSky: A Cordless Networking Solution for Palmtop Computers

Abstract

Palmtop computers are rapidly becoming the popular platform of choice for running personal productivity applications, but their networking capabilities are still lagging behind user expectations. Due to memory size, cost, and power considerations most palmtop computers support only limited form of point-to-point communication, namely, connection via a PSTN modem or a serial RS-232 cable. Due to wired point-to-point nature of these interfaces, satisfactory solutions for multi-point communication and direct LAN connection do not yet exist.. The BlueSky project aims at providing a low-cost, lowpower, indoor RF wireless networking solution for handheld devices. Our solution consists of two components; a BlueSky wireless attachment that plugs into the standard serial port of any palmtop device, and a LAN access point that acts as a layer 213 bridge between the wireless and the wired part of the network. Palmtop devices use dialup networking software and PPP to connect via BlueSky to the network. BlueSky enables MobileIP style seamless roaming between access points without requiring any changes to the communication stack of plamtop devices. Our roaming enhancements to PPP are implemented in the PPP server, the access point, and the BlueSky attachment, all of which are completely transparent to the palmtop device. In this paper, we present our design rationale and implementation experience of building the BlueSky system. We show in what ways low cost, low power, and form factor constraints affect the choice of protocols and function placement in wireless networking systems. We use PPP based mobility solution as an example to illustrate what design adjustments and compromises one has to make to build a working solution. Based on our experience, we recommend making a slight modification to the dialup networking stack of palmtop computers. Our proposed modification offers an efficient, lower cost, and lighter-weight wireless networking solution which is particularly attractive for enabling mobility over emerging short range, low power wireless technologies, such as IrDA, HomeRF and Bluetooth.